This invention relates to an automatic transmission control method and, more particularly, to a control method whereby the clutch disks and sun gears of a planetary gear train in an automatic transmission for an automotive vehicle are prevented from rotating at high speed when the transmission is shifted into the neutral range while the vehicle is traveling.
FIG. 5 illustrates a gear train of an automatic transmission useful in describing an example of the prior art. In order to shorten a time lag in shifting from the N range to the D range of the gear train when the vehicle having the transmission is at rest, it is arranged so that hydraulic pressure is introduced to a brake B3 even when the transmission is in the N range, as shown in Table 1 hereinbelow. The reason for this is that the stroke (or cylinder) volume of a brake generally is greater than that of a clutch. Even if the transmission is shifted to the N range while the vehicle is traveling, hydraulic pressure is still introduced to the brake B3 in a manner similar to that when the vehicle was at rest.
TABLE 1 ______________________________________ C1 C2 B1 B2 B3 ______________________________________ REV 0 0 1st 0 0 2nd 0 0 3rd 0 0 4th 0 0 N 0 ______________________________________
When hydraulic pressure is introduced to the brake B3 in shifting to the N range during vehicle travel, as in the prior art set forth above, the sun gear of the gear train rotate at a very high speed.
When the clutch disks and sun gears rotate at such a high speed owing to introduction of hydraulic pressure to the brake B3 in shifting to the N range during vehicle travel, service life is shortened due to rubbing together of the friction members, bearing life is shortened and the gears produce heat and noise.
Accordingly, an object of the present invention is to provide an automatic transmission control method whereby high-speed rotation of the clutch disks and sun gears in the transmission gear train is prevented when a shift is made to the N range during vehicle travel, thus making it possible to extend the lifetime of friction members and bearings and prevent the gears from producing heat and noise.
Other object of the present invention will become apparent in the entire disclosure.